1. Field of the Invention
The present invention relates to a process of forming shaped hollow semiconductor bodies, such as tubes composed of silicon or silicon carbide by depositing silicon or silicon carbide from a gaseous compound onto a heated substrate whereby the substrate is coated with a layer of, for example, silicon and, with the removal of the substrate, forms the desired hollow body.
2. Prior Art
German Auslegeschrift No. 1,805,970 teaches a method of manufacturing hollow bodies of silicon or silicon carbide by depositing silicon or silicon carbide from a gaseous compound onto the outer surface of a substrate composed of a heat-resistant material. After sufficient deposition, the substrate is removed, without destroying the hollow body defined by the deposited layer of silicon or silicon carbide. The substrate is preferably composed of graphite and is heated to the deposition temperature either inductively or by direct electrical conduction. The so-produced hollow silicon bodies are used in diffusion processes and are preferred over known diffusion ampules because they are of a higher purity. The preferred starting or depositing compound is silicochloroform (SiHCl.sub.3), which is decomposed at about 1050.degree. C. to 1250.degree. C. in a hydrogen atmosphere. The substrate utilized in manufacturing, for example silicon tubes, is preferably composed of graphite and is itself in the form of a hollow body. The substrate is removed, after its outer surface has been coated with a silicon layer, by heating the coated substrate in an oxygen-containing atmosphere so that the substrate is burnt out without destroying the outer silicon body.
In such methods, the reuse of the graphite substrate for additional tube manufacturing has been possible only on a restricted scale because the surface structure of graphite is substantially modified during its initial use, for example by polycrystalline silicon or silicon carbide inclusions therein.